Manufacturing method and composite powder metal rotor assembly for circumferential type interior permanent magnet machine

ABSTRACT

A composite powder metal disk for a rotor assembly in a circumferential type interior permanent magnet machine. The disk includes an inner ring of magnetically conducting powder metal compacted and sintered to a high density. The disk further includes an outer ring of permanent magnets separated by magnetically non-conducting powder metal compacted and sintered to a high density. The permanent magnets additionally are radially embedded by magnetically conducting powder metal compacted and sintered to a high density with optional intermediate non-conducting powder metal bridges extending radially from the permanent magnets to the outer surface of the disk. A rotor assembly is also provided having a plurality of the composite powder metal disks mounted axially along a shaft with their magnetic configurations aligned. A method for making the composite powder metal disks is further provided including filling a die with the powder metals, compacting the powders, and sintering the compacted powders.

FIELD OF THE INVENTION

This invention relates generally to interior permanent magnet machines,and more particularly, to the manufacture of rotors for acircumferential type interior permanent magnet machine.

BACKGROUND OF THE INVENTION

It is to be understood that the present invention relates to generatorsas well as to motors, however, to simplify the description that follows,a motor will be described with the understanding that the invention alsorelates to generators. With this understanding, there are two types ofinterior permanent magnet motors (IPM motors). In one type, the magnetslie orthogonally to the air gap between the rotor and stator, likespokes. In the other type, called circumferential IPM motors, themagnets face the air gap. Rotors for circumferential IPM motors havetypically been made with stacked stamped steel laminations andcircumferentially extending permanent magnets embedded in the interiorof the laminations. These circumferential IPM motors utilize narrowbridges, slits and air spaces within the rotor to substantially reducethe flux leakage that occurs and that would occur to a debilitatingdegree if these features were not incorporated into the rotor laminationdesign. These features greatly weaken the rotor, not allowing it torotate at medium high and high speeds, and still do not fully eliminatethe flux leakage.

There is thus a need to develop a circumferential type IPM machinehaving a structurally robust rotor operable at medium high and highspeeds with minimal rotor flux leakage, and preferably that may beproduced at a lower cost than that of currently fabricated IPM machines.

SUMMARY OF THE INVENTION

The present invention provides a composite powder metal disk for a rotorassembly in a circumferential type IPM machine, the disks having aninner annular magnetically conducting segment and an outer annularpermanent magnet segment. This outer annular segment includesalternating polarity permanent magnets separated in between bymagnetically non-conducting barrier segments. The permanent magnets arealso circumferentially embedded by radially outer magneticallyconducting segments, which may optionally include intermediatemagnetically non-conducting bridge segments extending from the permanentmagnets to an outer surface of the disk. The inner annular and outermagnetically conducting segments comprise soft ferromagnetic powdermetal compacted and sintered to a high density. The magneticallynon-conducting barrier segments and optional bridge segments comprisenon-ferromagnetic powder metal compacted and sintered to a high density.In a further embodiment, a rotor assembly is provided having a pluralityof the composite powder metal disks axially stacked along and mounted toa shaft. There is further provided a method of making such a compositepowder metal disk and rotor assembly in which a die is filled accordingto this desired magnetic pattern, followed by pressing the powder metalsand sintering the compacted powder metals to achieve a high densitycomposite powder metal disk of high structural stability. The permanentmagnets may comprise hard ferromagnetic powder metal pressed andsintered concurrently or sequentially with the soft ferromagnetic andnon-ferromagnetic powder metals, or may be prefabricated magnetsadhesively affixed or otherwise bound within the composite powder metaldisks after sintering the powder metal portions. These disks are thenstacked axially along a shaft with their magnetic patterns aligned toform the powder metal rotor assembly. A circumferential type IPM machineincorporating the powder metal rotor assembly of the present inventionexhibits increased power and speed capabilities, lower flux leakage, andmay be produced at a lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the principles ofthe invention.

FIG. 1 is a perspective view of a powder metal rotor assembly of thepresent invention having a plurality of disks stacked along a shaft,each having interior permanent magnets embedded by powder metalsegments;

FIG. 2 is a plan view of the rotor assembly of FIG. 1;

FIGS. 3-4 are plan views of alternative embodiments of powder metalrotor assemblies of the present invention having interior permanentmagnets;

FIG. 5 is a perspective view of an insert for use in a method of thepresent invention;

FIG. 6 is a perspective view of an inner bowl and outer bowl of a hopperthat may be used for the filling aspect of the present invention;

FIGS. 7A-7E are cross-sectional schematic views of a method of thepresent invention using the insert of FIG. 5 and the hopper of FIG. 6 toproduce the rotor assembly of FIGS. 1 and 2;

FIG. 8 is a perspective view of an insert for use in an alternativemethod of the present invention; and

FIGS. 9A-9C are cross-sectional schematic views of the present inventionusing the insert of FIG. 8 and the hopper of FIG. 6 to produce the rotorassembly of FIGS. 1 and 2.

DETAILED DESCRIPTION

The present invention provides composite powder metal rotor componentsfor rotor assemblies in circumferential type interior permanent magnetmachines. Permanent magnet machines incorporating the composite powdermetal components exhibit high power density and efficiency and highspeed rotating capability. To this end, and in accordance with thepresent invention, a plurality of powder metal disks or laminations arefabricated to comprise an inner annular magnetically conducting segmentand an outer annular permanent magnet segment or ring.

The outer annular permanent magnet segment comprises a plurality ofcircumferentially positioned permanent magnets of alternating polarityseparated by magnetically non-conducting segments. At the outer face ofthe permanent magnets, between the non-conducting barrier segments, aremagnetically conducting segments referred to herein as radially outermagnetically conducting segments. These conducting segments togetherwith the non-conducting barrier segments embed the permanent magnetswithin the disk. Each radially outer magnetically conducting segment mayfurther include an intermediate non-conducting bridge segment thatextends radially from the permanent magnet to the outer circumferentialsurface of the disk.

The inner annular and radially outer magnetically conducting segmentscomprise a pressed and sintered soft ferromagnetic powder metal. In anembodiment of the present invention, the soft ferromagnetic powder metalis nickel, iron, cobalt or an alloy thereof. In another embodiment ofthe present invention, this soft ferromagnetic metal is a low carbonsteel or a high purity iron powder with a minor addition of phosphorus,such as covered by MPIF (Metal Powder Industry Federation) Standard 35F-0000, which contains approximately 0.27% phosphorus. In general, AISI400 series stainless steels are magnetically conducting, and may be usedin the present invention.

The outer annular permanent magnet segment or ring comprises a series ofalternating polarity permanent magnets, such as ferrite or rare earthpermanent magnets. Depending on the particular machine, it is within theskill of one in the art to determine the appropriate number and size ofpermanent magnets to be circumferentially spaced around an interiorportion of the disk. The permanent magnets may be either prefabricatedmagnets affixed to the inner annular segment and the magneticallynon-conducting barrier segments, or pressed and sintered hardferromagnetic powder metal.

The magnetically non-conducting barrier and bridge segments comprisepressed and sintered non-ferromagnetic powder metal. In an embodiment ofthe present invention, the non-ferromagnetic powder metal is austeniticstainless steel, such as SS316. In general, the AISI 300 seriesstainless steels are non-magnetic and may be used in the presentinvention. Also, the AISI 8000 series steels are non-magnetic and may beused.

In an embodiment of the present invention, the ferromagnetic metal ofthe inner annular and radially outer magnetically conducting segmentsand the non-ferromagnetic metal of the magnetically non-conductingbarrier and bridge segments in the outer annular permanent magnetsegment are chosen so as to have similar densities and sinteringtemperatures, and are approximately of the same strength, such that uponcompaction and sintering, the materials behave in a similar fashion. Inan embodiment of the present invention, the soft ferromagnetic powdermetal is Fe-0.27%P and the non-ferromagnetic powder metal is SS316.

The inner annular magnetically conducting segment may optionally furthercomprise a magnetically non-conducting insert positioned to surround ashaft in the rotor assembly. This insert comprises non-ferromagneticpowder metal as described above in the outer annular permanent magnetsegment. The insert functions to insulate the hub and shaft frommagnetic flux. The insert may further have a star-shaped configurationdesigned to enhance the flux between the magnets, as will be shown anddescribed further below.

The powder metal disks of the present invention typically exhibitmagnetically conducting segments having at least about 95% oftheoretical density, and typically between about 95%-98% of theoreticaldensity. Wrought steel or iron has a theoretical density of about 7.85gms/cm³, and thus, the magnetically conducting segment exhibits adensity of around 7.46-7.69 gms/cm³. The optional non-conductingsegments of the powder metal disks of the present invention exhibit adensity of at least about 85% of theoretical density, which is on theorder of about 6.7 gms/cm³. Thus, the non-ferromagnetic powder metalsare less compactible then the ferromagnetic powder metals. The pressedand sintered hard ferromagnetic powder metal magnets of certainembodiments of the present invention exhibit a density of at least95.5%±about 3.5% of theoretical density, depending on fill factor, whichis on the order of about 3.8-7.0 gms/cm³.

The powder metal disks or rings can essentially be of any thickness.These disks are aligned axially along a shaft and mounted to the shaftto form a rotor assembly. The shaft is typically equipped with a key andthe individual disks have a keyway on an interior surface to align thedisks to the shaft upon attaching the part to the shaft. In anembodiment of the present invention, the individual disks or rings havea thickness on the order of about d-f inches. As disk thicknessincreases, the boundaries between the powder metal conducting segmentand powder metal non-conducting segments or inserts may begin to blur.In practice, up to 13 disks of the present invention having a d-f inchthickness are suitable for forming a rotor assembly. There is, however,no limit to the thickness of each disk or the number of disks that maybe utilized to construct a rotor assembly. The individual disks arealigned with respect to each other along the shaft such that themagnetic flux paths are aligned along the shaft. The non-ferromagneticpowder metal acts as an insulator between the aligned flux pathscomprised of the soft ferromagnetic powder metal segment and thepermanent magnets. This arrangement allows better direction of magneticflux and improves the torque capability of the machine.

With reference to the Figures in which like numerals are used throughoutto represent like parts, FIGS. 1 and 2 depict in perspective view andplan view, respectively, a powder metal rotor assembly 10 of the presentinvention having a plurality of powder metal composite disks 12 stackedalong a shaft 14, each disk 12 having an inner annular magneticallyconducting segment 16 and an outer annular permanent magnet segment orring 18 comprising a plurality of alternating polarity circumferentiallyextending permanent magnets 20. The disks are aligned from one disk 12to another along the length of the shaft 14.

The outer annular permanent magnet segment 18 includes magneticallynon-conducting barrier segments 22 separating the permanent magnets 20.The non-conducting barrier segments 22 provide insulation that directsthe magnetic flux from one permanent magnet 20 to the next alternatingpolarity permanent magnet 20. This configuration enhances the magneticflux in the air gap. The permanent magnet segment 18 further includes aradially outer magnetically conducting segment 24 adjacent eachpermanent magnet 20 that embeds the permanent magnet 20 in the disk 12.Each radially outer magnetically conducting segment 24 may include anintermediate magnetically non-conducting bridge segment 26 that extendsradially from a respective permanent magnet 20 to an outercircumferential surface 28 of disk 12. Each bridge segment 26essentially cuts its respective radially outer magnetically conductingsegment 24 in two.

Alternatively, disk 12 can be made without the inner annularmagnetically conducting segment 16. Thus, disk 12 would comprise a ring18 of alternating polarity circumferentially extending permanent magnets20 separated by magnetically non-conducting barrier segments 22 andpartially embedded by radially outer magnetically conducting segments24, with or without bridge segments 26. Disk 12 is then assembled onto asleeve or cylinder, with or without a separate wrought or machinedshaft.

FIG. 3 depicts a disk similar in configuration to that depicted in FIGS.1 and 2, but includes a magnetically non-conducting insert 30 in theinner annular segment 16. Insert 30 may have an essentially star-shapedconfiguration and extends from the interior surface 29 of the disk 12into tip portions 30 a or 30 b that terminate at (30 a) or near (30 b) arespective permanent magnet 20 in the outer annular permanent magnetsegment 18. As can be seen, the magnetically conducting portion 16 a ofthe inner annular magnetically conducting segment 16 directs magneticflux from one permanent magnet 20 to the next alternating polaritypermanent magnet 20. The insert 30 further blocks magnetic flux frombeing channeled into the shaft 14.

In FIG. 4, the composite powder metal disk 12 is similar to thatdepicted in FIGS. 1 and 2, but the disk 12 further includes an innerannular magnetically non-conducting insert 32 adjacent the interiorsurface 29 of the disk 12. As with the insert 30 of FIG. 3, insert 32blocks magnetic flux from being channeled into the shaft 14. FIG. 4 alsodepicts an embodiment in which the radially outer magneticallyconducting segments 24 do not include intermediate bridge segments.

While FIGS. 1-4 depict various embodiments for a circumferential typeinterior permanent magnet rotor, it should be appreciated that numerousother embodiments exist having a varying number of permanent magnets,and having various sizes of permanent magnets, as well as varying sizesfor the non-conducting segments separating the permanent magnets, andthe conducting segments embedding the magnets. Thus, the inventionshould not be limited to the particular embodiments shown in FIGS. 1-4.It should be further understood that each embodiment described as a diskcould be formed as a ring, which is generally understood to have asmaller annular width and larger inner diameter than a disk. Thus, theterm disk used throughout the description of the invention and in theclaims hereafter is hereby defined to include a ring. Further, the termdisk includes solid disks. The aperture in the center of the disk thatreceives the rotor shaft may be later formed, for example, by machining.

The present invention further provides a method for fabricatingcomposite powder metal disks or rings for assembling into a rotor for acircumferential type interior permanent magnet machine. To this end, andin accordance with the present invention, a disk-shaped die is providedhaving discrete regions in a pattern corresponding to the desired rotormagnetic configuration. An inner annular region is filled with a softferromagnetic powder metal to ultimately form the inner annularmagnetically conducting segment of the rotor, when included. In an outerannular portion of the die, a plurality of discrete regions are alsofilled with the soft ferromagnetic powder metal to ultimately form theradially outer magnetically conducting segments. Another plurality ofdiscrete regions in the outer annular portion of the die are filled withnon-ferromagnetic powder metal to ultimately form the magneticallynon-conducting barrier and bridge segments of the rotor. In anembodiment in which the permanent magnets comprise hard ferromagneticpowder metal, yet another plurality of discrete regions in the outerannular portion of the die are filled with hard ferromagnetic powdermetal. Alternatively, removable dummy inserts may be used to form spacesin which prefabricated permanent magnets may later be affixed.

The powder metals are pressed in the die to form a compacted powdermetal disk. This compacted powder metal is then sintered to form apowder metal disk or lamination having an inner annular region ofmagnetically conducting material and an outer annular region ofpermanent magnets embedded by non-conducting and conducting materials,the disk exhibiting high structural stability. The pressing andsintering processes result in magnetically conducting segments having adensity of at least about 95% of theoretical density, non-conductingsegments having a density of at least about 85% of theoretical densityand permanent magnets having a density of at least 95.5%±about 3.5% oftheoretical density (depending on fill factor). The method for formingthese rotors provides increased mechanical integrity, reduced fluxleakage, more efficient flux channeling, reduced cost and simplerconstruction.

For alternative embodiments of a disk of the present invention, such asshown in FIGS. 3 and 4, a non-ferromagnetic powder metal is filled intothe die in a desired pattern in the inner annular portion to ultimatelyform the non-conducting inserts.

The method of the present invention may thus include filling a die withtwo or three dissimilar powder metals. At the least, the die ispartially filled in outer annular portions with a soft ferromagneticpowder metal and a non-ferromagnetic powder metal. For certainembodiments of the present invention, the die may also be filled with asoft ferromagnetic powder metal and a non-ferromagnetic powder metal inregions of the inner annular portion of the die. For other alternativeembodiments of the present invention, the die may be filled with a hardferromagnetic powder metal in regions of the outer annular portion ofthe die.

In one embodiment of the present invention using two or three dissimilarpowder metals, the regions in the die are filled concurrently with thevarious powder metals, which are then concurrently pressed and sintered.In another embodiment of the present invention also using two or threedissimilar powder metals, the regions are filled sequentially with thepowder metal being pressed and then sintered after each filling step. Inother words, one powder metal is filled, pressed and sintered, and thenthe second powder metal is filled and the entire assembly is pressed andsintered, and then the optional third powder metal is filled and theentire assembly is pressed and sintered.

The pressing of the filled powder metal may be accomplished byuniaxially pressing the powder in a die, for example at a pressure ofabout 45-50 tsi. It should be understood that the pressure needed isdependent upon the particular powder metal materials that are chosen. Ina further embodiment of the present invention, the pressing of thepowder metal involves heating the die to a temperature in the range ofabout 275° F. (135° C.) to about 290° F. (143° C.), and heating thepowders within the die to a temperature about 175° F. (79° C.) to about225° F. (107° C.).

In an embodiment of the present invention, the sintering of the pressedpowder comprises heating the compacted powder metal to a firsttemperature of about 1400° F. (760° C.) and holding at that temperaturefor about one hour. Generally, the powder metal includes a lubricatingmaterial, such as a plastic, on the particles to increase the strengthof the material during compaction. The internal lubricant reducesparticle-to-particle friction, thus allowing the compacted powder toachieve a higher green strength after sintering. The lubricant is thenburned out of the composite during this initial sintering operation,also known as a delubrication or delubing step. A delubing for one houris a general standard practice in the industry and it should beappreciated that times above or below one hour are sufficient for thepurposes of the present invention if delubrication is achieved thereby.Likewise, the temperature may be varied from the general industrystandard if the ultimate delubing function is performed thereby.

After delubing, the sintering temperature is raised to a full sinteringtemperature, which is generally in the industry about 2050° F. (1121°C.). During this full sintering, the compacted powder shrinks, andparticle-to-particle bonds are formed, generally between iron particles.Standard industry practice involves full sintering for a period of onehour, but it should be understood that the sintering time andtemperature may be adjusted as necessary. The sintering operation may beperformed in a vacuum furnace, and the furnace may be filled with acontrolled atmosphere, such as argon, nitrogen, hydrogen or combinationsthereof. Alternatively, the sintering process may be performed in acontinuous belt furnace, which is also generally provided with acontrolled atmosphere, for example a hydrogen/nitrogen atmosphere suchas 75% H₂/25% N₂. Other types of furnaces and furnace atmospheres may beused within the scope of the present invention as determined by oneskilled in the art.

For the purpose of illustrating the method of the present invention,FIGS. 5-9C depict die inserts, hopper configurations and pressingtechniques that may be used to achieve the concurrent filling orsequential filling of the powder metals and subsequent compaction toform the composite powder metal disks of the present invention. It is tobe understood, however, that these illustrations are merely examples ofpossible methods for carrying out the present invention.

FIG. 5 depicts a die insert 40 that may be placed within a die cavity toproduce the powder metal disk 12 of FIGS. 1 and 2 in which the permanentmagnets are prefabricated and affixed in the composite disk 12 aftercompaction and sintering of the powder metals. The two powder metals,i.e. the soft ferromagnetic and non-ferromagnetic powder metals, arefilled concurrently or sequentially into the separate insert cavities42, 44, 46, 48, and then the insert 40 is removed. Spacing or dummyinserts 50 may be used in cavities 52 to form spaces between thenon-conducting barrier segments 22 into which the permanent magnets 20may subsequently be inserted and affixed. By way of example only, FIG. 6depicts a hopper assembly 60 that may be used to fill the insert 40 ofFIG. 5 with the powder metals. In this assembly 60, an inner bowl 62 isprovided having a plurality of tubes 64, 66 for forming thenon-conducting barrier and bridge segments 22, 26, respectively, of thecomposite part or metal disk 12 of FIGS. 1 and 2. This inner bowl 62 isadapted to hold and deliver the non-ferromagnetic powder metal. An outerbowl 68 is positioned around the inner bowl 62, with the outer bowl 68adapted to hold and deliver soft ferromagnetic powder metal. This dualhopper assembly 60 enables either concurrent or sequential filling ofthe die insert 40 of FIG. 5.

FIGS. 7A-7E depict schematic views in partial cross-section taken alongline 7A—7A of FIG. 5 of how the die insert 40 of FIG. 5 and the hopperassembly 60 of FIG. 6 can be used with an uniaxial die press 70 toproduce the composite powder metal disk 12 of FIGS. 1 and 2. In thismethod, the insert 40 is placed within a cavity 72 in the die 74, asshown in FIG. 7A, with a lower punch 76 of the press 70 abutting thebottom 40 a of the insert 40. The hopper assembly 60 is placed over theinsert 40 and the powder metals 43, 47 are filled into the insertcavities 42, 44, 46, 48, concurrently or sequentially, as shown in FIG.7B. The hopper assembly 60 is then removed, leaving a filled insert 40in the die cavity 72, as shown in FIG. 7C. Then the insert 40 is liftedout of the die cavity 72, which causes some settling of the powder, asseen in FIG. 7D. The upper punch 78 of the press 70 is then lowered downupon the powder-filled die cavity 72, as shown by the arrow in FIG. 7D,to uniaxially press the powders in the die cavity 72. The finalcomposite part 80 is then ejected from the die cavity 72 by raising thelower punch 76 and the part 80 is transferred to a sintering furnace(not shown). Where the filling is sequential, the first powder is pouredinto either the inner bowl 62 or outer bowl 68, and a speciallyconfigured upper punch 78 is lowered so as to press the filled powder,and the partially filled and compacted insert (not shown) is sintered.The second fill is then effected and the insert 40 removed for pressing,ejection and sintering of the complete part 80.

FIG. 8 depicts an alternative die insert 40′ that may be placed on a topsurface 75 of the die 74 over the die cavity 72 to again form the powdermetal disk 12 depicted in FIGS. 1 and 2. FIGS. 9A-9C show in partialcross-section taken along line 9A—9A of FIG. 8 the method for using theinsert 40′ of FIG. 8. The insert is set on top surface 75 of the die 74over the cavity 72 with the lower punch 76 in the ejection position, asshown in FIG. 9A. The powder metals 43, 47 are then filled into theinsert 40′, either concurrently or sequentially, as shown in FIG. 7B,and the lower punch 76 is then lowered to the fill position. Thelowering of the punch 76 forms a vacuum which pulls the powder metals43, 47 out of the bottom 40 a′ of the insert 40′ and into the die cavity72, as shown in FIG. 9B. The insert 40′ is then removed from the topsurface 75 of the die 74, and the upper punch 78 is lowered into the diecavity 72 to compact the powder metals 43, 47. The lower punch 76 isthen raised to eject the final composite part 80, as shown in FIG. 9C,and the part 80 is then transferred to a sintering furnace (not shown).Where the filling is sequential, dummy placement segments (not shown)may be used if needed for the first filling/pressing/sintering sequencewhich can then be removed to effect the filling of the second powdermetal.

In one embodiment of the present invention, pneumatic air hammers ortappers (not shown) may be placed on, in, or around the inserts 40, 40′used in either the method depicted in FIGS. 7A-7E or the method depictedin FIGS. 9A-9C. The vibrating of the insert 40, 40′ enables the powdermetal 43, 47 to flow out of the insert 40, 40′ with greater ease as theinsert 40, 40′ is removed, and further enables a greater tap density. Inanother embodiment of the present invention, a dry lube is sprayed oradded to the inside of the insert cavities 42, 44, 46, 48 used in eitherof those methods. Again, this dry lube helps to improve the flow of thepowder metals 43, 47 out of the insert 40, 40′. In yet anotherembodiment of the present invention, heaters and thermocouples (notshown) may be used in conjunction with the insert 40, 40′. The heatkeeps the powder warm, if warm compaction is being optimized, and againallows the powder metals 43, 47 to more easily flow out of the insert40, 40′.

It should be further understood that while the methods shown anddescribed herein are discussed with respect to forming a solid compositedisk in which an aperture may be machined in the center after compactionor sintering for receiving the shaft of a rotor assembly, the compositepart may be formed as a disk with the aperture already formed in thecenter. Likewise, the outer annular segment 18 may be first formed as asolid ring of pressed and sintered non-ferromagnetic and softferromagnetic powder metals, then subsequently machined to form spacesinto which permanent magnets may be inserted.

For an embodiment of the present invention in which the permanentmagnets are pressed and sintered hard ferromagnetic powder metal, athree-hopper assembly may be used to achieve a tri-fill process. Insertcavities 52 would be filled with the hard ferromagnetic powder metal. Aswith the dual-fill process described above, the tri-fill process caninclude concurrent filling of the powder metals or sequential filling ofthe powder metals.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, they are not intended to restrict or in any waylimit the scope of the appended claims to such detail. Additionaladvantages and modifications will readily appear to those skilled in theart. For example, variations in the hopper assembly, filling method anddie inserts may be employed to achieve a composite powder metal disk ofthe present invention, and variations in the magnetic configuration ofthe disks other than that shown in the Figures herein are well withinthe scope of the present invention. The invention in its broader aspectsis therefore not limited to the specific details, representativeapparatuses and methods and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the scope or spirit of applicant's general inventive concept.

1. A method of making a powder metal rotor for a circumferential typeinterior permanent magnet machine, the method comprising: filling aplurality of discrete first regions within an outer annular region of adisk-shaped die with a non-ferromagnetic powder metal in solidparticulate form so as to leave spaces between each discrete firstregion; filling a plurality of discrete second regions in the outerannular region between the first regions with a soft ferromagneticpowder metal in solid particulate form so as to maintain a radiallyinner circumferentially extending space between each discrete firstregion; pressing the solid particulate form powders in the die to form acompacted powder metal disk; sintering the compacted powder metal disk;and providing permanent magnets in the radially inner circumferentiallyextending spaces between the discrete first regions of the outer annularregion in an arrangement of alternating polarity to form a compositepowder metal disk having a plurality of alternating polarity permanentmagnets separated by magnetically non-conducting barrier segments andradially embedded by magnetically conducting segments.
 2. The method ofclaim 1 further comprising filling an inner annular region of the diewith a soft ferromagnetic powder metal in solid particulate form to formthe disk further having an inner annular magnetically conductingsegment.
 3. The method of claim 1, wherein all the regions are filledconcurrently.
 4. The method of claim 1, wherein all the regions arefilled sequentially with the powder metal being pressed and sinteredafter each filling step.
 5. The method of claim 1, wherein the providingof permanent magnets includes affixing prefabricated permanent magnetsto the barrier segments.
 6. The method of claim 1, wherein the providingof permanent magnets includes filling the radially innercircumferentially extending spaces with a hard ferromagnetic powdermetal in solid particulate form, pressing the hard ferromagnetic powdermetal and sintering the pressed powder.
 7. The method of claim 1,wherein the soft ferromagnetic powder metal is Ni, Fe, Co or an alloythereof.
 8. The method of claim 1, wherein the soft ferromagnetic powdermetal is a high purity iron powder with a minor addition of phosphorus.9. The method of claim 1, wherein the non-ferromagnetic powder metal isan austenitic stainless steel.
 10. The method of claim 1, wherein thenon-ferromagnetic powder metal is an AISI 8000 series steel.
 11. Themethod of claim 1, wherein the pressing comprises uniaxially pressingthe powders in the die.
 12. The method of claim 1, wherein the pressingcomprises pre-heating the powders and pre-heating the die.
 13. Themethod of claim 1, wherein, after the pressing, the compacted powdermetal disk is delubricated at a first temperature, followed by sinteringat a second temperature greater than the first temperature.
 14. Themethod of claim 1 further comprising filling the discrete second regionsso as to further maintain a radially extending unfilled region througheach discrete second region and filling the radially extending unfilledregions with a non-ferromagnetic powder metal, in solid particulate formpressing the non-ferromagnetic powder metal, and sintering the pressedpowder to form intermediate magnetically non-conducting bridge segmentsin the magnetically conducting segments.
 15. A method of making a powdermetal rotor for a circumferential type interior permanent magnetmachine, the method comprising: filling an inner annular region of adisk-shaped die with a soft ferromagnetic powder metal in solidparticulate form; filling a plurality of discrete first regions withinan outer annular region of the die with a non-ferromagnetic powder metalin solid particulate form so as to leave spaces between each discretefirst region; filling a plurality of discrete second regions in theouter annular region between the first regions with a soft ferromagneticpowder metal in solid particulate form so as to maintain a radiallyinner circumferentially extending space between each discrete firstregion; pressing the solid particulate form powders in the die to form acompacted powder metal disk; sintering the compacted powder metal disk;and providing permanent magnets in the radially inner circumferentiallyextending spaces between the discrete first regions of the outer annularregion in an arrangement of alternating polarity to form a compositepowder metal disk having an inner annular magnetically conductingsegment and an outer annular permanent magnet segment of a plurality ofalternating polarity permanent magnets separated by magneticallynon-conducting barrier segments and radially embedded by magneticallyconducting segments.
 16. The method of claim 15, wherein all the regionsare filled concurrently.
 17. The method of claim 15, wherein all theregions are filled sequentially with the powder metal being pressed andsintered after each filling step.
 18. The method of claim 15, whereinthe providing of permanent magnets includes affixing prefabricatedpermanent magnets to the inner segment.
 19. The method of claim 15,wherein the providing of permanent magnets includes filling the radiallyinner circumferentially extending spaces with a hard ferromagneticpowder metal in solid particulate form, pressing the hard ferromagneticpowder metal and sintering the pressed powder.
 20. The method of claim15, wherein the soft ferromagnetic powder metal is Ni, Fe, Co or analloy thereof.
 21. The method of claim 15, wherein the softferromagnetic powder metal is a high purity iron powder with a minoraddition of phosphorus.
 22. The method of claim 15, wherein thenon-ferromagnetic powder metal is an austenitic stainless steel.
 23. Themethod of claim 15, wherein the non-ferromagnetic powder metal is anAISI 8000 series steel.
 24. The method of claim 15, wherein the pressingcomprises uniaxially pressing the powders in the die.
 25. The method ofclaim 15, wherein the pressing comprises pre-heating the powders andpre-heating the die.
 26. The method of claim 15, wherein, after thepressing, the compacted powder metal disk is delubricated at a firsttemperature, followed by sintering at a second temperature greater thanthe first temperature.
 27. The method of claim 15, wherein the sinteringis performed in a vacuum furnace having a controlled atmosphere.
 28. Themethod of claim 15, wherein the sintering is performed in a belt furnacehaving a controlled atmosphere.
 29. The method of claim 15 furthercomprising filling the discrete second regions so as to further maintaina radially extending unfilled region through each discrete second regionand filling the radially extending unfilled regions with anon-ferromagnetic powder metal in solid particulate form, pressing thenon-ferromagnetic powder metal, and sintering the pressed powder to formintermediate magnetically non-conducting bridge segments in themagnetically conducting segments of the outer annular permanent magnetsegment.
 30. The method of claim 15 further comprising filling a portionof the inner annular region in a desired pattern with anon-ferromagnetic powder metal in solid particulate form, pressing thenon-ferromagnetic powder metal, and sintering the pressed powder to forman inner magnetically non-conducting insert.
 31. The method of claim 15further comprising stacking a plurality of the composite powder metaldisks axially along a shaft to form a powder metal rotor assembly.
 32. Amethod of making a powder metal rotor for a circumferential typeinterior permanent magnet machine, the method comprising: filling aninner annular region and a plurality of first portions of an outerannular region of a disk-shaped die with a soft ferromagnetic powdermetal in solid particulate form, pressing and sintering the softferromagnetic powder metal in the die to form a compacted and sinteredinner annular magnetically conducting segment and a plurality ofcompacted and sintered outer magnetically conducting segments; filling aplurality of second portions in the outer annular region of the die witha non-ferromagnetic powder metal in solid particulate form, the secondportions being in alternating relation with the outer magneticallyconducting segments; pressing the non-ferromagnetic powder metal in thedie to form a plurality of compacted magnetically non-conducting barriersegments; sintering the compacted magnetically non-conducting barriersegments and the compacted and sintered inner annular and outermagnetically conducting segments; and providing circumferentiallyextending permanent magnets in a plurality of radially inner fourthportions in the outer annular region between the magneticallynon-conducting barrier segments in an arrangement of alternatingpolarity to form a composite powder metal disk having an inner annularmagnetically conducting segment and an outer annular permanent magnetsegment of a plurality of alternating polarity permanent magnetsseparated by magnetically non-conducting barrier segments and radiallyembedded by magnetically conducting segments.
 33. The method of claim32, wherein the providing step includes, after the second sinteringstep, filling the fourth portions with a hard ferromagnetic powdermetal, pressing the hard ferromagnetic powder metal in the die to form aplurality of compacted permanent magnet segments, and sintering thecompacted permanent magnet segments and the compacted and sintered innerannular and outer conducting segments and magnetically non-conductingbarrier segments.
 34. The method of claim 32 further comprising affixingprefabricated permanent magnets of alternating polarity in the fourthportions between the magnetically non-conducting barrier segments. 35.The method of claim 32, wherein the soft ferromagnetic powder metal isNi, Fe, Co or an alloy thereof.
 36. The method of claim 32, wherein thesoft ferromagnetic powder metal is a high purity iron powder with aminor addition of phosphorus.
 37. The method of claim 32, wherein thenon-ferromagnetic powder metal is an austenitic stainless steel.
 38. Themethod of claim 32, wherein the non-ferromagnetic powder metal is anAISI 8000 series steel.
 39. The method of claim 32, wherein eachpressing comprises uniaxially pressing the powder in the die.
 40. Themethod of claim 32, wherein each pressing comprises pre-heating thepowder and pre-heating the die.
 41. The method of claim 32, wherein,after each pressing, the compacted segments are delubricated at a firsttemperature, followed by sintering at a second temperature greater thanthe first temperature.
 42. The method of claim 32, wherein eachsintering is performed in a vacuum furnace having a controlledatmosphere.
 43. The method of claim 32, wherein each sintering isperformed in a belt furnace having a controlled atmosphere.
 44. Themethod of claim 32 further comprising stacking a plurality of thecomposite powder metal disks axially along a shaft to form a powdermetal rotor assembly.
 45. A method of making a powder metal rotor for acircumferential type interior permanent magnet machine, the methodcomprising: filling an inner annular region and a plurality of firstportions of an outer annular region of a disk-shaped die with a softferromagnetic powder metal; pressing and sintering the softferromagnetic powder metal in the die to form a compacted and sinteredinner annular magnetically conducting segment and a plurality ofcompacted and sintered outer magnetically conducting segments; filling aplurality of second portions in the outer annular region of the die witha non-ferromagnetic powder metal, the second portions being inalternating relation with the outer magnetically conducting segments;filling a plurality of third portions in the outer annular region of thedie with a non-ferromagnetic powder metal, the third portions radiallyextending through an intermediate portion of each first portion;pressing the non-ferromagnetic powder metal in the die to form aplurality of compacted magnetically non-conducting barrier segments andbridge segments; sintering the compacted magnetically non-conductingbarrier and bridge segments and the compacted and sintered inner annularand outer magnetically conducting segments; and providingcircumferentially extending permanent magnets in a plurality of radiallyinner fourth portions in the outer annular region between themagnetically non-conducting barrier segments in an arrangement ofalternating polarity to form a composite powder metal disk having aninner annular magnetically conducting segment and an outer annularpermanent magnet segment of a plurality of alternating polaritypermanent magnets separated by magnetically non-conducting barriersegments and radially embedded by magnetically conducting segments withintermediate magnetically non-conducting bridge segments.
 46. The methodof claim 45, wherein the providing step includes, after the secondsintering step, filling the fourth portions with a hard ferromagneticpowder metal, pressing the hard ferromagnetic powder metal in the die toform a plurality of compacted permanent magnet segments, and sinteringthe compacted permanent magnet segments and the compacted and sinteredinner annular and outer conducting segments and magneticallynon-conducting barrier and bridge segments.
 47. The method of claim 45further comprising affixing prefabricated permanent magnets ofalternating polarity in the fourth portions between the magneticallynon-conducting barrier segments.
 48. The method of claim 45, wherein thesoft ferromagnetic powder metal is Ni, Fe, Co or an alloy thereof. 49.The method of claim 45, wherein the soft ferromagnetic powder metal is ahigh purity iron powder with a minor addition of phosphorus.
 50. Themethod of claim 45, wherein the non-ferromagnetic powder metal is anaustenitic stainless steel.
 51. The method of claim 45, wherein thenon-ferromagnetic powder metal is an AISI 8000 series steel.
 52. Themethod of claim 45, wherein each pressing comprises uniaxially pressingthe powder in the die.
 53. The method of claim 45, wherein each pressingcomprises pre-heating the powder and pre-heating the die.
 54. The methodof claim 45, wherein, after each pressing, the compacted segments aredelubricated at a first temperature, followed by sintering at a secondtemperature greater than the first temperature.
 55. The method of claim45, wherein each sintering is performed in a vacuum furnace having acontrolled atmosphere.
 56. The method of claim 45, wherein eachsintering is performed in a belt furnace having a controlled atmosphere.57. The method of claim 45 further comprising stacking a plurality ofthe composite powder metal disks axially along a shaft to form a powdermetal rotor assembly.
 58. A method of making a powder metal rotor for acircumferential type interior permanent magnet machine, the methodcomprising: filling a plurality of discrete first regions within anouter annular region of a disk-shaped die with a non-ferromagneticpowder metal so as to leave spaces between each discrete first region;filling a plurality of discrete second regions in the outer annularregion between the first regions with a soft ferromagnetic powder metalso as to maintain a radially inner circumferentially extending spacebetween each discrete first region while maintaining a radiallyextending unfilled region through each discrete second region andfilling the radially extending unfilled regions with a non-ferromagneticpowder metal; pressing the powders in the die to form a compacted powdermetal disk; sintering the compacted powder metal disk; and providingpermanent magnets in the radially inner circumferentially extendingspaces between the discrete first regions of the outer annular region inan arrangement of alternating polarity to form a composite powder metaldisk having a plurality of alternating polarity permanent magnetsseparated by magnetically non-conducting barrier segments and radiallyembedded by magnetically conducting segments with intermediatemagnetically non-conducting bridge segments.
 59. A method of making apowder metal rotor for a circumferential type interior permanent magnetmachine, the method comprising: filling an inner annular region of adisk-shaped die with a soft ferromagnetic powder metal; filling aplurality of discrete first regions within an outer annular region ofthe die with a non-ferromagnetic powder metal so as to leave spacesbetween each discrete first region; filling a plurality of discretesecond regions in the outer annular region between the first regionswith a soft ferromagnetic powder metal so as to maintain a radiallyinner circumferentially extending space between each discrete firstregion while maintaining a radially extending unfilled region througheach discrete second region and filling the radially extending unfilledregions with a non-ferromagnetic powder metal; pressing the powders inthe die to form a compacted powder metal disk; sintering the compactedpowder metal disk; and providing permanent magnets in the radially innercircumferentially extending spaces between the discrete first regions ofthe outer annular region in an arrangement of alternating polarity toform a composite powder metal disk having an inner annular magneticallyconducting segment and an outer annular permanent magnet segment of aplurality of alternating polarity permanent magnets separated bymagnetically non-conducting barrier segments and radially embedded bymagnetically conducting segments with intermediate magneticallynon-conducting bridge segments.
 60. A method of making a powder metalrotor for a circumferential type interior permanent magnet machine, themethod comprising: filling an inner annular region of a disk-shaped diewith a soft ferromagnetic powder metal; filling a portion of the innerannular region in a desired pattern with a non-ferromagnetic powdermetal; filling a plurality of discrete first regions within an outerannular region of the die with a non-ferromagnetic powder metal so as toleave spaces between each discrete first region; filling a plurality ofdiscrete second regions in the outer annular region between the firstregions with a soft ferromagnetic powder metal so as to maintain aradially inner circumferentially extending space between each discretefirst region; pressing the powders in the die to form a compacted powdermetal disk; sintering the compacted powder metal disk; and providingpermanent magnets in the radially inner circumferentially extendingspaces between the discrete first regions of the outer annular region inan arrangement of alternating polarity to form a composite powder metaldisk having an inner annular magnetically conducting segment with aninner magnetically non-conducting insert and an outer annular permanentmagnet segment of a plurality of alternating polarity permanent magnetsseparated by magnetically non-conducting barrier segments and radiallyembedded by magnetically conducting segments.